Does friendly fire hurt the candidates?

Republicans this morning launched a well-planned attack on Barack Obama using statements fellow Democrats have made questioning his readiness for the presidency — all fair game, but it raises the question why such an attack never worked for Democrats against John McCain.

One reason is few Republicans argued McCain wasn’t prepared to be commander-in-chief, arguably the most serious part of the role of president. Whatever his specific positions, McCain brings as much experience for that role as anyone since President Eisenhower.

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The one attack Democrats have seized on came as McCain was facing pressure from Mitt Romney over the economy, but it was a self-inflicted shot: McCain acknowledged that the economy wasn’t his strongest suit.

But maybe the best explanation is that Democrats were reluctant to use many of the attacks. So many of them came from the right, accusing McCain of not being conservative enough. That’s hardly an argument Democrats would want to make about the man they’re trying to portray as a clone of President Bush.

Given that Democrats’ attacks on Obama mostly focus on readiness, they may have slightly better luck in tarnishing the apparent Democratic nominee. Highlighting Hillary Rodham Clinton’s attack on Obama’s health care plan isn’t likely to get Republicans very far, but using her criticism of his willingness to negotiate with enemy leaders could be powerful.